The human eye provides vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a crystalline lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye and the transparency of the cornea and the lens. When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light that can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial intraocular lens (TOL).
Cataractous lenses may be removed using a surgical technique called phacoemulsification. A typical surgical probe used in phacoemulsification procedures includes a handpiece or handheld probe having an ultrasonically driven cutting needle. During the procedure, a surgeon brings the tip of the cutting needle into contact with the lens of the eye. The cutting needle rapidly vibrates such that contact with tip fragments the lens. Throughout the procedure, irrigating fluid is delivered into the eye. Fluid including the lens fragments is also aspirated out of the eye. In some instances, the cutting needle includes an aspiration lumen through which the fluid is aspirated. The fluid may be aspirated from the eye, through the aspiration lumen, through elastic tubing, and to a drain reservoir.
A common phenomenon during a phacoemulsification procedure arises from a blockage, or occlusion, of the aspiration lumen. As the irrigation fluid and lens fragments are aspirated away from the interior of the eye through the aspiration lumen of the cutting needle, pieces of tissue that are larger than the diameter of the aspiration lumen may occlude or clog the aspiration lumen, particularly at the opening of the aspiration lumen at the tip of the cutting needle. While the aspiration lumen is clogged, vacuum pressure builds up, causing collapse of the elastic tubing. When occlusion is cleared, an undesirably large quantity of fluid and tissue may be drawn from the eye into the aspiration lumen too quickly. This is known as post-occlusion surge. The post-occlusion surge can, in some cases, cause the eye to collapse and/or the lens capsule to be torn.